The present invention concerns compositions useful in the preparation of catalysts, the catalysts and the polymerization of olefins employing these catalysts.
Dual transition metal compounds containing both chromium and titanium have been employed in the preparation of catalysts for olefin polymerization in U.S. Pat. Nos. 3,752,795 and 3,847,957. Such dual transition metal compounds are formed by reacting a tetraorganotitanate with chromium oxide.
Typically, catalysts which employ a chromium compound to polymerize ethylene show a sizeable response to both hydrogen and temperature. As a result, most catalyst systems containing chromium must be run at low reaction temperatures (i.e., slurry conditions) to prevent the formation of large amounts of undesirable low molecular weight waxes or high melt index polyethylene.
In a co-pending application, it has been shown that the reaction product of tetravalent hydrocarbyloxy zirconium compounds with oxygen-containing chromium compounds, when added to a Ziegler-type catalyst, is useful in the polymerization of .alpha.-olefins to produce polymers having a high molecular weight and a narrow molecular weight distribution. It has now been discovered that hydrocarbon-soluble compounds of zirconium and chromium, and especially combinations of these compounds, can be employed in catalysts to lead to unexpectedly high molecular weights and narrow molecular weight distributions without the necessity of thermally reacting the compounds prior to catalyst addition.